help!

About the powder mildew. not just the leaves which are gone now also the smaller stems that has it. the main stems and trunk doesnt.  i found the recipe for baking soda and water spray. will that kill the exsisting leaves that are green?  i googled it last night and found about ten answers and some try water and some dont.  im at a loss, was hoping to talk to someone on this forum that has personal experience with this, if you know anyone please let me know. thanks.